Buried mines pose a hazard not only to military personnel in time of war, but also to non-combatants during time of peace. Indeed, many children each year are injured or killed by mines that are the lingering reminders of conflicts that have long since been resolved.
Thus mines, frequently buried by the thousands, remain threats to humans for prolonged periods, unless and until they are removed or otherwise neutralized. Accordingly, it is important to detect mines during and after armed conflict for subsequent neutralization of the mines.
It happens that many mines, particularly newer mines, are made mostly of plastic. This complicates the detection process, which is typically based on metal detection principles. It happens that even plastic mines incorporate small metal components such as steel firing pins and copper igniter cups, but discriminating such small components from other small metal objects buried in the vicinity of the mine is difficult.
With this in mind, it is perhaps not surprising that previous mine detection systems do not detect and classify plastic mines as readily as might be hoped. For example, U.S. Pat. No. 5,596,277 discloses a system that displays return signals as a function of phase to discriminate "good" targets from "bad", but the '277 patent teaches that a "good" target optimally will have a single phase angle range. Consequently, the '277 invention will only discriminate one type of metal from another, but not one type of metal in a mine from the same type of metal lying in the ground near the mine. Likewise, other mine detection systems of which the present patentee is aware cannot adequately discriminate small metal components of mostly-plastic mines from surrounding metal objects.
The present invention, however, fortuitously recognizes that it is possible to find and classify plastic mines. As recognized herein, plastic mines typically have two or more components that are made of dissimilar metals, with the size and composition of the metal components varying from mine to mine. The present invention further recognizes that the combination of the responses from the metal components of a plastic mine can be used to classify the responses as being unique to a particular type of mine. It is the object of the present invention to address one or more of the above-noted problems in an effective and cost-efficient way.